1. Field of Invention:
This invention relates to interface apparatus and methods of operation in communication networks. More particularly, the invention relates to adaptive interface apparatus and methods for data terminal elements transmitting and receiving Ethernet over a shielded twisted pair cabling system.
2. Description of Prior Art:
Many customers have installed Shielded Twisted Pair (STP) cabling systems. The systems have specific characteristics based on a 150 ohm STP wire with hermaphroditic data connectors, and a standard RJ 45 telephone connector with a unique pin out. The system further includes a large data connectors installed at an office wall connector and has the RJ 45 telephone connector in a wiring closet. Workstations in these offices typically have token ring adapters with cables that attach them from the workstation adapter to the telephone connector in the office wall connector and wiring closet.
Ethernet installations include 10/100BASE T Ethernet adapters, which provides dual speed connection to the Ethernet at 10 Mbps or 100 Mbps. The 10/100BASE T Ethernet adapters use RJ 45 standard telephone connectors throughout the network. However, the telephone connector pin out is different than that used for token ring. Also, the Ethernet adapter uses Unshielded Twisted Pair (UTP) 100-ohm cabling.
Token ring customers using STP cabling systems may wish the option to connect to Ethernet installation and to do so presents several problems. First, the pin out of the standard RJ 45 telephone connectors in the STP cabling system is different than the pin out of an Ethernet telephone connector. Second, there is a difference in the characteristic impedance used by the STP cabling system (150 ohm) and a typical Ethernet installation (100-ohm). Third testing or replacing the cabling system will, in most cases, eliminate any potential cost savings in using Ethernet. Fourth, many Ethernet transceivers have adaptive equalization algorithms, which are designed assuming that the transmission media is Unshielded Twisted Pair (UTP) Category 5 cable. STP cabling systems have less attenuation and phase shift than the UTP Category 5 cable for a given length. Some commercial transceivers are known to be optimized around the midlength cable (20 meters 80 meters). The Ethernet algorithms which change both equalizer and attenuation settings in these transceivers are designed assuming that the transceiver will be used in a cabling system using up to 100 meters of UTP Category 5 cable. While many transceivers may function with type 1 STP cabling, it would be advantageous to have the capability of inserting a filter which emulates a given number of meters of UTP 5 cable for those transceivers which optimize around the 100 meter design point.
What is needed in the communication industry is an adaptive interface, which makes the STP cabling system easily usable for Ethernet installations and satisfies all Ethernet requirements.
Prior art related to interface apparatus and networks includes the following:
U.S. Pat. No. 5,497,460 to W. D. Bailey et al., issued Mar. 5, 1996 (Bailey), discloses a multiprotocol LAN adapter for use in a workstation to determine the type of network to which the workstation is connected to through a port and automatically determine the type of physical medium to which the workstation is attached. Connected to each port are various network interfaces for supporting various available networking protocols, e.g., token ring, Ethernet, etc. Logic circuitry and control software are connected to the network interface device. To determine the network connection to the port, a short interrogation frame is successively transmitted by each of the networking interface devices to each of the ports. Depending upon the status of each transmission, the adapter determines what type of network, if any is connected to by which type of physical media. Based upon these two determinations, the workstation can be automatically configured without user intervention.
U.S. Pat. No. 5,249,183 to D. Wong et al., issued Sep. 28, 1993 (Wong), discloses a local area network (LAN) having a 10 BASE-T media attachment unit (MAU) coupling an attachment unit interface (AUI) to a twisted pair link through an AUI port of the 10 BASE-T MAU. The MAU provides an interface between the AUI and a RJ 45 twisted pair telephone connector which auto engages which activity is detected on the twisted pair link. Lack of activity on the twisted pair link forces the 10 BASE-T MAU to isolate its AUI port from the AUI. An Ethernet (coaxial) type MAU commonly connected with the 10 BASE-T MAU at the AUI may be utilized without manual intervention when the twisted pair link is inactive.
None of the prior art discloses interface apparatus with specific pin-to-pin transformation from the RJ 45 side to the STP connector side; impedance transformation and a lumped element passive filter which emulates the amplitude attenuation and phase effect of a given number of meters of UTP Category 5 cable.